Permineralization preserves biological material when minerals precipitate in its pores or internal spaces. Filling spaces in wood or bone can support and retain details of the original cellular architecture. This differs from replacing the original substance with a new mineral, although both processes can occur in one fossil.
Experiments placing wood in silica-bearing hot-spring water documented deposition of silica within the spaces of the tissue. Such observations connect a recognizable fossilization mechanism to mineral-bearing water entering a porous biological structure.[ref]
Rapid wood silicification in hot spring water: an explanation of silicification of wood during the Earth's history by Hisatada Akahane and others. Sedimentary Geology, 2004; experimental wood fragments and silica deposition in cell lumina
The speed observed in one chemical environment is not a universal clock for permineralization; composition, fluid access and subsequent alteration differ among deposits. New to topics? Read the docs here!